Corporate mobility should be more than carrying a device for e-mail and Web access, another for voice calls and another for urgent alerts. Mobility should offer a consistent, quality user experience with converged business applications that users can easily access in many ways ⬠both wired and wireless.

The fixed frontier of the enterprise network is giving way to a new 'mobile frontier' a new way of connecting users to information. The mobile frontier transcends the enterprise network perimeter, appearing wherever the user needs access to information on the campus, in a regional or branch office, at retail outlets, at home and on the road.

The mobile frontier makes use of existing high-speed networks the corporate LAN, the corporate WAN, and the Internet. It does not replace these existing networks, but deploys on top of them as a service overlay, preventing disruptive equipment changes and preserving investment. At the same time, the mobile frontier permits a large-scale reduction in cost for the wired network through port consolidation, reduced equipment needs, reduced power requirements, and the elimination of move/add/change costs.

VoIP has become a major technology trend, as enterprises consolidate multiple services onto a single converged network. Even after migrating to VoIP, some network managers find that users do not actually use the expensive voice networks they have installed. Instead, an increasing number of users provide their mobile phone number to business contacts so that they can be reached when not at their desks. These employees then bill their employer for the cost of the mobile phone, since it is used for business.

For many enterprises and applications, the optimum solution may be a combination of Wi-Fi and cellular. A Wi-Fi/cellular roaming solution requires dual-mode handsets that support both Voice over Wi-Fi (VoWiFi) and cellular - and a network gateway. The gateway manages access and handoff and connects to both a mobile switching centre for cellular calls and a data network for WLAN calls. As people move within range of a wireless access point, the gateway authorises access and delivers both voice and data network services over the WLAN. When people move outside of coverage of the current WLAN, the gateway seamlessly switches control over to another WLAN or a cellular network if another WLAN is not available.

Nearly all major network operators worldwide are deploying Wi-Fi-based hotspots and a large number of them such as AT&T, British Telecom, NTT Docomo, SBC, Sprint, and Verizon are also offering VoIP. Therefore, the ideal mobile device for these established operators will be capable of dual mode voice operation (cellular + VoWiFi). This device will roam seamlessly between cell to cell, from WLAN to WLAN and from cell to WLAN. Infonetics Research has reported that that 50% of service providers worldwide plan to offer packetised voice services in 2006

Dual mode devices emerge

On the mobile frontier, voice is the killer app. Combining VoIP and mobility in a VoWiFi service provides all the mobility benefits of cellular with the cost savings of VoIP and does not require expensive power upgrades to wiring closets. Newer dual-mode voice handsets operate over the enterprise wireless LAN wherever it is available, and over the public cellular network everywhere else.

There are several technical requirements for the support of dual mode handsets on the mobile frontier:

End-to-end Quality of Service: When voice and data traffic are combined on a link, the voice packets must be given priority to ensure their delivery without undue delay, regardless of the volume of data traffic on the link. In order to provide a suitable network for voice, every link end-to-end in the call path must be QoS-enabled, including the WAN, the LAN and the mobile frontier.

Flexible authentication methods: While the state-of-the art in authentication (WPA2) is considered adequately secure for enterprise use, many VoWiFi handsets only support older authentication methods, such as static WEP and MAC address. The network manager faces a choice: either wait for handset technology to catch up with PC implementations, or allow older devices access to the network, but in a very restricted manner, to avoid exposing the enterprise network to hackers impersonating handsets.

End-to-end encryption for the voice call. Users consider voice calls to be confidential: they do not expect to be overheard. However, conventional WLAN architectures allow anyone with access to the wired LAN to intercept and decode calls. While IP PBX vendors are moving slowly to encrypt voice traffic, the mobile frontier can already protect calls originating from VoWiFi handsets.

Seamless vertical roaming

Vertical roaming, or handover between two different types of networks (e.g. from 802.11a to 802.11b or from any WLAN technology to GPRS/UMTS/CDMA) has many intricate technical issues that need to be resolved. Challenges include what happens when you roam onto a network whose quality is either higher or lower than the quality of the network you were just in? How do you navigate varying qualities of service? Most difficult of all, how to you navigate different roaming policies and prices?

Device clients for fast handoff

Mobi Client is software for phones and PDAs that allows a user to place and receive a call using a single number, on the same handset, over the best available network WiFi or cellular. Calls are routed via the best available network; e.g. when the WiFi signal in a hotspot fades the call will be handover. This process is automatic and seamless, so users are shielded from issues regarding network usage and selection. However, it has the regular look-and-feel along with its own phonebook. The corporate directory is readily available to users over the WiFi or cellular data interface for click-to-call service regardless of local or optimal network coverage.

Handset vendors are pushing the technology in order to stay competitive with each other, and carriers will likely co-operate because they expect customers to demand the convenience of roaming. Service providers are also likely to co-operate because it is less expensive for them to support handoffs between cellular and WiFi than to build more capacity in their cellular networks.

So, if wireless calls can be handed off to WiFi networks at convention centres or other public areas with large crowds, the WiFi networks can pass the calls off to landline networks for transport. The alternative would be to build more expensive cellular stations at these sites.